21820505 has 16 divisors (see below), whose sum is σ = 30167040. Its totient is φ = 14841792.

The previous prime is 21820489. The next prime is 21820517. The reversal of 21820505 is 50502812.

It is not a de Polignac number, because 21820505 - 2⁴ = 21820489 is a prime.

It is a super-2 number, since 2×21820505² = 952268876910050, which contains 22 as substring.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 1991 + ... + 6899.

It is an arithmetic number, because the mean of its divisors is an integer number (1885440).

Almost surely, 2^21820505 is an apocalyptic number.

It is an amenable number.

21820505 is a deficient number, since it is larger than the sum of its proper divisors (8346535).

21820505 is a wasteful number, since it uses less digits than its factorization.

21820505 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5048.

The product of its (nonzero) digits is 800, while the sum is 23.

The square root of 21820505 is about 4671.2423401061. The cubic root of 21820505 is about 279.4398025767.

The spelling of 21820505 in words is "twenty-one million, eight hundred twenty thousand, five hundred five".